Methods and systems for polishing pad control

ABSTRACT

A polishing assembly for polishing of silicon wafers is provided. The polishing assembly includes a polishing pad, a polishing head assembly, a temperature sensor, and a controller. The polishing head assembly holds a silicon wafer to position the silicon wafer in contact with the polishing pad. The polishing head assembly selectively varies a removal profile of the silicon wafer. The temperature sensor collects thermal data from a portion of the polishing pad. The controller is communicatively coupled to the polishing head assembly and the temperature sensor. The controller receives the thermal data from the temperature sensor and operates the polishing head assembly to selectively vary the removal profile of the silicon wafer based at least in part on the thermal data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/186,821 filed Jun. 30, 2015, and U.S. patent application Ser. No.15/190,624, filed Jun. 23, 2016, both of which are hereby incorporatedby reference in their entirety.

FIELD

This disclosure relates generally to polishing of semiconductor or solarwafers and more particularly to single side polishing apparatus andmethods for controlling flatness of the wafer.

BACKGROUND

Semiconductor wafers are commonly used in the production of integratedcircuit (IC) chips on which circuitry are printed. The circuitry isfirst printed in miniaturized form onto surfaces of the wafers. Thewafers are then broken into circuit chips. This miniaturized circuitryrequires that front and back surfaces of each wafer be extremely flatand parallel to ensure that the circuitry can be properly printed overthe entire surface of the wafer. To accomplish this, grinding andpolishing processes are commonly used to improve flatness andparallelism of the front and back surfaces of the wafer after the waferis cut from an ingot. A particularly good finish is required whenpolishing the wafer in preparation for printing the miniaturizedcircuits on the wafer by an electron beam-lithographic orphotolithographic process (hereinafter “lithography”). The wafer surfaceon which the miniaturized circuits are to be printed must be flat.Similarly, flatness and finish are also important for solarapplications.

Polishing machines typically include a circular or annular polishing padmounted on a turntable or platen for driven rotation about a verticalaxis passing through the center of the pad and a mechanism for holdingthe wafer and forcing it into the polishing pad. The wafer is typicallymounted to the polishing head using for example, liquid surface tensionor a vacuum/suction. A polishing slurry, typically including chemicalpolishing agents and abrasive particles, is applied to the pad forgreater polishing interaction between the polishing pad and the surfaceof the wafer. This type of polishing operation is typically referred toas chemical-mechanical polishing (CMP).

During operation, the pad is rotated and the wafer is brought intocontact with and forced against the pad by the polishing head. As thepad wears, e.g., after a few hundred wafers, wafer flatness parametersdegrade because the pad is no longer flat, but instead has a wornannular band forming a depression along the polishing surface of thepad. Such pad wear impacts wafer flatness, and may cause “dishing” or“doming” or a combination thereof resulting in a “w-shape”.

Some known systems adjust wafer flatness during single-side polishing tochange the vacuum used to hold the block to which the wafer is attachedin order to introduce a variation of the curvature of the block and theattached wafer. An increase of the vacuum will result in a concavedeformation of the block and of the wafer, the wafer edge will bepolished more than the wafer center, resulting in a more convex (lessconcave) wafer. On the contrary, a reduction of the vacuum will resultin a more concave (less convex) wafer. This approach assumes that thecurrent wafer shape (concave or convex) produced by the polisher isknown. In general, however, the wafer shape is measured after polishing,so that the current wafer shape knowledge always has a delay, resultingin an inaccurate feedback to the vacuum adjustment system.

This Background section is intended to introduce the reader to variousaspects of art that may be related to various aspects of the presentdisclosure, which are described and/or claimed below. This discussion isbelieved to be helpful in providing the reader with backgroundinformation to facilitate a better understanding of the various aspectsof the present disclosure. Accordingly, it should be understood thatthese statements are to be read in this light, and not as admissions ofprior art.

SUMMARY

In one aspect, a method for varying a removal profile of a silicon waferduring polishing using a polishing apparatus is provided. The polishingapparatus includes a polishing pad, a polishing head assembly configuredto hold the silicon wafer, a temperature sensor, and a controller. Themethod includes receiving, at the controller, thermal data of a portionof the polishing pad from the temperature sensor and determining, by thecontroller, the removal profile of the silicon wafer based at least inpart on the thermal data. The method further includes operating, by thecontroller, the polishing head assembly to position the silicon wafer incontact with the polishing pad and to selectively vary the removalprofile of the silicon wafer based at least in part on the thermal data.

In another aspect, a polishing assembly for polishing of silicon wafersis provided. The polishing assembly includes a polishing pad, apolishing head assembly, a temperature sensor, and a controller. Thepolishing head assembly holds a silicon wafer to position the siliconwafer in contact with the polishing pad. The polishing head assemblyselectively varies a removal profile of the silicon wafer. Thetemperature sensor collects thermal data from a portion of the polishingpad. The controller is communicatively coupled to the polishing headassembly and the temperature sensor. The controller receives the thermaldata from the temperature sensor and selectively varies the removalprofile of the silicon wafer based at least in part on the thermal data.

In yet another aspect, a non-transitory computer-readable storage mediahaving computer-executable instructions embodied thereon is provided.When executed by at least one processor, the computer-executableinstructions cause the processor to receive thermal data of a portion ofa polishing pad from a temperature sensor and determine a removalprofile of a silicon wafer based at least in part on the thermal data.The computer-executable instructions cause the processor to operate apolishing head assembly to position the silicon wafer in contact withthe polishing pad and to selectively vary the removal profile of thesilicon wafer based at least in part on the thermal data.

Various refinements exist of the features noted in relation to theabove-mentioned aspects. Further features may also be incorporated inthe above-mentioned aspects as well. These refinements and additionalfeatures may exist individually or in any combination. For instance,various features discussed below in relation to any of the illustratedembodiments may be incorporated into any of the above-described aspects,alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic elevation of a single side polisher;

FIG. 2 is a side view of a polishing head assembly in a firstconfiguration implemented by the single side polisher of FIG. 1;

FIG. 3 is a side view of a polishing head assembly in a secondconfiguration implemented by the single side polisher of FIG. 1;

FIG. 4 is a side view of a polishing head assembly in a thirdconfiguration implemented by the single side polisher of FIG. 1;

FIG. 5 is a side view of a polishing head assembly in a fourthconfiguration implemented by the single side polisher of FIG. 1;

FIG. 6 is a block diagram of an example embodiment of a computing devicesuitable for use with the single side polisher of FIG. 1;

FIG. 7 is a top view of a single side polisher such as the single sidepolisher of FIG. 1;

FIG. 8 is an example diagram of a relationship between a removal profileof a silicon wafer and an average temperature curve that may be measuredfrom the single side polisher shown in FIG. 1;

FIG. 9 is an example average temperature profile of a silicon waferproduced by the single side polisher shown in FIG. 1;

FIG. 10 is a closer view of the average temperature profile shown inFIG. 9 and, more specifically, a second portion of the averagetemperature profile;

FIG. 11 is a method for varying a removal profile of a wafer duringpolishing using the polishing apparatus shown in FIG. 1;

FIG. 12 is a graph of an example experiment using the single sidepolisher shown in FIG. 1;

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Generally, and in one embodiment of the present disclosure, a wafer thathas previously been rough polished so that it has rough front and backsurfaces is first subjected to an intermediate polishing operation inwhich the front surface of the wafer, but not the back surface, ispolished to improve flatness parameters or to smooth the front surfaceand remove handling scratches. To carry out this operation, the wafer isplaced against the polishing head. In this embodiment, the wafer isretained in position against the polishing head by surface tension. Thewafer also is placed on a turntable of a machine with the front surfaceof the wafer contacting the polishing surface of a polishing pad.

A polishing head mounted on the machine is capable of vertical movementalong an axis extending through the wafer. While the turntable rotates,the polishing head is moved against the wafer to urge the wafer towardthe turntable, thereby pressing the front surface of the wafer intopolishing engagement with the polishing surface of the polishing pad.

A conventional polishing slurry containing abrasive particles and achemical etchant is applied to the polishing pad. The polishing padworks the slurry against the surface of the wafer to remove materialfrom the front surface of the wafer, resulting in a surface of improvedsmoothness. As an example, the intermediate polishing operationpreferably removes less than about 1 micron of material from the frontside of the wafer.

The wafer is then subjected to a finish polishing operation in which thefront surface of the wafer is finish polished to remove fine or “micro”scratches caused by large size colloidal silica, such as Syton® fromDuPont Air Products Nanomaterials, LLC, in the intermediate step and toproduce a highly reflective, damage-free front surface of the wafer. Theintermediate polishing operation generally removes more of the waferthan the finishing polishing operation. The wafer may be finish polishedin the same single-side polishing machine used to intermediate polishthe wafer as described above. However, a separate single-side polishingmachine may also be used for the finish polishing operation. A finishpolishing slurry typically has an ammonia base and a reducedconcentration of colloidal silica is injected between the polishing padand the wafer. The polishing pad works the finish polishing slurryagainst the front surface of the wafer to remove any remaining scratchesand haze so that the front surface of the wafer is generallyhighly-reflective and damage free.

Referring to FIG. 1, a portion of a single side polishing apparatus isshown schematically and indicated generally at 100. The single sidepolisher 100 may be used to polish a front surface of semiconductorwafers W. It is contemplated that other types of single side polishingapparatus may be used.

The polishing apparatus 100 includes a wafer holding mechanism, e.g., abacking film 110, a retaining ring 120, a polishing head assembly 130,and a turntable 140 having a polishing pad 150. The backing film 110 islocated between a polishing head assembly 130 and the retaining ring120, which receives a wafer W. The retaining ring 120 has at least onecircular opening to receive the wafer W to be polished therein. Thewafer W of this embodiment is retained against the polishing headassembly 130 by surface tension.

The polishing apparatus 100 applies a force to the polishing headassembly 130 to move the polishing head assembly vertically to raise andlower the polishing head assembly 130 with respect to the wafer W andthe turntable 140. An upward force raises the polishing head assembly130, and a downward force lowers the polishing head assembly. Asdiscussed above, the downward vertical movement of the polishing headassembly 130 against the wafer W provides the polishing pressure to thewafer to urge the wafer into the polishing pad 150 of the turntable 140.As the polishing apparatus 100 increases the downward force, thepolishing head assembly 130 moves vertically lower to increase thepolishing pressure.

A portion of the polishing head assembly 130 and polishing pad 150 andturntable 140 are rotated at selected rotation speeds by a suitabledrive mechanism (not shown) as is known in the art. The rotationalspeeds of the polishing pad and the turntable may be the same ordifferent. The apparatus 100 includes a controller 155 that controlsoperation of apparatus 100 as described herein. For example, thecontroller 155 allows the operator to select rotation speeds for boththe polishing head assembly 130 and the turntable 140, and the downwardforce applied to the polishing head assembly 130.

The apparatus 100 includes a pressurizing source 180 to manipulate avacuum pressure of the polishing head assembly 130 as described below.In the example embodiment, the controller 155 is communicatively coupledto the pressurizing source 180 to selectively vary the pressure of thepolishing head assembly 130.

With reference to FIGS. 2-5, the polishing head assembly 130 includes apolishing head 160 and a cap 170. The cap is suitably made of plastic,aluminum, steel, ceramic, such as alumina or silicon carbide, or anysuitable material with sufficient stiffness, including coated silicon.

The cap 170 includes a plate or floor 172 surrounded by an annular wall174 extending upward therefrom. In use, the backing film 110 attachesthe wafer W to the floor 172. In a natural or un-deflected state, thefloor 172 has a concave shape (relative to the chamber), such that thecenter of the floor is lower than the perimeter. In other embodiments,the natural state of the floor 172 may be any shape such as a flat shapeor a convex shape (relative to the chamber). The floor 172 is capable oftemporarily deflecting without permanently deforming. In the exampleembodiment, the floor 172 is about 0.118 to about 0.275 inches (3-7 mm)thick, or about 0.625 inches (16 mm) thick for plastic, and has adiameter of about 5.905 to about 6.496 inches (150-165 mm).

The annular wall 174 is rigidly attached to and extends downward from anedge 162 of the polishing head 160. Together the polishing head 160 andthe cap 170 form a downwardly domed structure defining a chamber 176.The cap 170 may be attached to the polishing head 160 with bolts orother suitable fasteners. In other embodiments, an adhesive, such as anepoxy, is used to attach the cap 170 to the edge 162 of the polishinghead 160.

In the example embodiment, chamber 176 is connected with thepressurizing source 180 to vary the pressure within the chamber 176. Thepressure within the chamber 176 is varied to vary the shape of the floor172. The cap 170 contacts the wafer W. Thus, varying the pressure withinthe chamber 176 to change the shape of the floor 172 causes a resultingchange in the force distribution across the wafer W and thereby causesthe wafer to bend in response. The change in force distribution alsocauses a change in the rate of removal of material from the wafer W.Generally, the rate of removal is increased at portions of the wafer Wthat transfer relatively greater force to the polishing pad 150.

As a result, the pressure within the chamber 176 may be controlled bythe pressurizing source 180 to increase or decrease the shape of thefloor 172 of the cap 170 and thereby adjust the amount of doming ordishing of the wafer. As the pressure within the chamber 176 isdecreased, the floor 172 transitions from a natural, un-deflected,concave shape (shown in FIG. 2) to a flat shape (shown in FIG. 3) thatis substantially parallel with a bottom surface of the polishing head160, and finally to an upwardly curved or convex shape (shown in FIG.5).

As shown in FIG. 3, a given or predetermined pressure P within thechamber 176 shapes the floor 172 to be substantially flat, resulting ina removal profile that is also substantially flat. As shown in FIG. 4,increasing the pressure within the chamber 176 to, for example, 1.1 Pcauses both the floor 172 and the removal profile to become downwardlycurved. As shown in FIG. 5, decreasing the pressure within the chamberto, for example, 0.9 P causes both the shape of the floor 172 and theremoval profile to become dished. Suitably, the change in pressurewithin the chamber 176 may range from about 0.7 P to about 1.3 P. Thus,a change in pressure within the chamber 176 provides an operator with acontrol variable and the ability to adjust the polished shape of thewafer W. In some embodiments, the predetermined polishing pressure mayrange from 1.0 psi to 4.0 psi. In other embodiments, the predeterminedpolishing pressure may be less than 6.0 psi.

In some embodiments, additionally or alternatively, the shape of thefloor 172 is controlled by varying the amount of downward pressure onthe polishing head assembly. Downward movement of the polishing headassembly 130 toward the polishing pad 150 deflects the floor 172 upwardtoward the polishing head 160. The direction of deflection isperpendicular to the top surface of the wafer W. As the pressure of thecap 170 against the wafer W increases, the magnitude of deflection ofthe cap 170 also increases. Regulation of the polishing pressure allowsthe deflection of the floor 172 to be increased or decreased. As thedeflection of the floor 172 is changed, the shape of the floor is alsochanged. For example, as the polishing pressure is increased, the floor172 transitions from a natural, un-deflected or downwardly curved orconcave shape shown in FIG. 2 to a flat shape shown in FIG. 3 that issubstantially parallel with a bottom surface of the polishing head 160,and finally to an upwardly curved or convex shape shown in FIG. 5.

FIG. 6 is a block diagram of an example embodiment of a computing device600 suitable for use with the polishing apparatus 100 of FIG. 1. Forexample, computing device 600 is representative of the controller 155shown and described above with reference to FIG. 1. The computing device600 includes a processor 605 for executing instructions. In someembodiments, executable instructions are stored in a memory area 610.The processor 605 may include one or more processing units (e.g., in amulti-core configuration). The memory area 610 is any device allowinginformation such as executable instructions and/or data to be stored andretrieved. The memory area 610 may include one or more computer readablestorage devices or other computer readable media, including transitoryand non-transitory computer readable media.

In at least some implementations, the computing device 600 also includesat least one media output component 615 for presenting information to auser 601. The media output component 615 is any component capable ofconveying information to the user 601. In some embodiments, the mediaoutput component 615 includes an output adapter such as a video adapterand/or an audio adapter. An output adapter is operatively connected tothe processor 605 and operatively connectable to an output device suchas a display device (e.g., a liquid crystal display (LCD), organic lightemitting diode (OLED) display, cathode ray tube (CRT), or “electronicink” display) or an audio output device (e.g., a speaker or headphones).In some embodiments, at least one such display device and/or audiodevice is included in the media output component 615.

In some embodiments, the computing device 600 includes an input device620 for receiving input from the user 601. The input device 620 mayinclude, for example, a keyboard, a pointing device, a mouse, a stylus,a touch sensitive panel (e.g., a touch pad or a touch screen), agyroscope, an accelerometer, a position detector, or an audio inputdevice. A single component such as a touch screen may function as bothan output device of the media output component 415 and the input device620.

The computing device 600 may also include a communication interface 625,which may be communicatively connected to one or more remote devices.The communication interface 625 may include, for example, a wired orwireless network adapter or a wireless data transceiver for use with amobile phone network (e.g., Global System for Mobile communications(GSM), 3G, 4G or Bluetooth) or other mobile data network (e.g.,Worldwide Interoperability for Microwave Access (WIMAX)).

Stored in the memory area 610 are, for example, processor-executableinstructions for providing a user interface to the user 601 via mediaoutput component 615 and, optionally, receiving and processing inputfrom the input device 620. The memory area 610 may include, but is notlimited to, any computer-operated hardware suitable for storing and/orretrieving processor-executable instructions and/or data. The memoryarea 610 may include random access memory (RAM) such as dynamic RAM(DRAM) or static RAM (SRAM), read-only memory (ROM), erasableprogrammable read-only memory (EPROM), electrically erasableprogrammable read-only memory (EEPROM), and non-volatile RAM (NVRAM).Further, the memory area 610 may include multiple storage units such ashard disks or solid state disks in a redundant array of inexpensivedisks (RAID) configuration. The memory area 610 may include a storagearea network (SAN) and/or a network attached storage (NAS) system. Insome embodiments, the memory area 610 includes memory that is integratedin the computing device 600. For example, the computing device 600 mayinclude one or more hard disk drives as the memory area 610. The memoryarea 610 may also include memory that is external to the computingdevice 600 and may be accessed by a plurality of computing devices. Theabove memory types are exemplary only, and are thus not limiting as tothe types of memory usable for storage of processor-executableinstructions and/or data.

FIG. 7 is a top view of part of an example polishing apparatus 700.Polishing apparatus 700 is similar to polishing apparatus 100 and, inthe absence of a contrary representation, the same reference numbersidentify the same or similar elements. The contact between the polishingapparatus 700 and the wafer W while rotating generates heat in thepolishing pad 150. By measuring the radial temperature profile of thepolishing pad 150, the current profile of the wafer W may be determinedas described below.

The polishing apparatus 700 includes a temperature sensor 710 configuredto measure a temperature of the polishing pad 150. The exampletemperature sensor 710 is positioned adjacent the polishing pad 150.Alternatively, the temperature sensor 710 may be positioned above,below, or integrated in the polishing pad 150. In some embodiments, thepolishing apparatus 700 includes a plurality of temperature sensors 710.In the example embodiment, the temperature sensor 710 is an infrared(IR) sensor (e.g., an IR camera). Alternatively, the temperature sensor710 may be any type of temperature sensor such as, but not limited to, athermocouple, a resistive temperature device (RTDs), a bimetallicdevice, a thermometer, a change-of-state sensor, and a silicon diodesensor. The temperature sensor 710 may be coupled to or adjacent to thepolishing pad 150 in an alternative location (e.g., within the polishingpad 150) to facilitate the temperature sensor 710 capturing thermaldata. The thermal data may include, for example, a temperature gradientas a function of distance or time, differential thermal data, aplurality of discrete temperatures, or one or more heat maps. In theexample embodiment, the thermal data is transmitted as a temperaturegradient over a distance from the edge to the center of the polishingpad 150.

The temperature sensor 710 does not rotate with the polishing pad 150 inthe example embodiment. In alternative embodiments, the temperaturesensor 710 rotates with the polishing pad 150. The temperature sensor710 is positioned to capture the thermal data from at least a segment ofthe polishing pad 150. In some embodiments, the temperature sensor 710measures the thermal data of a segment along a first diameter 720. Inthe example embodiment, the temperature sensor 710 measures atemperature of a first radius 725 of the first diameter 720.Alternatively, the temperature sensor 710 may capture the thermal dataalong other locations of the polishing pad 150 such as a seconddiameter, a chord, another linear portion of the polishing pad 150, oran area of the polishing pad 150 (e.g., a non-linear portion).

The temperature sensor 710 is communicatively coupled to the controller155. Alternatively, the temperature sensor 710 may be communicativelycoupled to a remote computing device (not shown) in communication withthe controller 155. The temperature sensor 710 captures the thermal dataand transmits the thermal data to the controller 155 (not shown in FIG.7). For each wafer, the temperature sensor 710 captures a plurality ofsets of thermal data while the wafer is being polished. The controller155 receives the sets of thermal data from the temperature sensor andgenerates an average temperature profile (sometimes also referred to asan “average temperature curve”) by averaging the sets of thermal datatogether. In some embodiments, the temperature sensor 710 captures andtransmits one set of thermal data. In other embodiments, the temperaturesensor 710 captures the thermal data, generates the average temperatureprofile, and transmits the average temperature profile to the controller155 in addition to or in place of the thermal data.

The controller 155 is configured to determine the removal profile of thewafer W based on the average temperature profile as described below. Ifthe controller 155 determines that the polishing pad is removingmaterial in a manner that will result in a wafer W that is not flat(i.e., concave or convex), the controller 155 alters the operation ofthe polishing apparatus 700 such as signaling the pressurizing source180 to change the pressure with the chamber 176 of the polishing headassembly 130 to make the wafer W flat.

More specifically, the controller 155 controls the removal profile bycomparing a differential temperature determined from the averagetemperature profiles to a reference differential temperature thatrepresents a flat removal profile for a silicon wafer. The controller155 determines a differential temperature for a wafer W using itsaverage temperature profile. The controller 155 averages thedifferential temperatures from one or more wafers and compares theaveraged differential temperature to the reference differentialtemperature. By averaging the differential temperatures, the controller155 does not overcompensate the adjustments of the polishing apparatus700 in response to data collected from each wafer. If the averageddifferential temperature and the reference differential temperature arenot substantially the same, the removal profiles of the wafers may notbe flat. The controller 155 adjusts the vacuum pressure on the polishinghead assembly 130 using the comparison of the differential temperaturesas feedback. In the example embodiment, the averaged differentialtemperature stabilizes at the reference differential temperature.

FIG. 8 is an example diagram 800 of the relationship between the removalprofile of a wafer and an average temperature curve that may be measuredfrom a single side polishing apparatus shown in FIG. 1. The removalprofile is indicated by the differential temperature between the maximumtemperature and a lower temperature measured at a distance from thepoint of the maximum temperature as described further below. In theexample embodiment, the wafer is centrally located relative the averagetemperature curve (i.e., the center of the wafer substantially coincideswith the peak of the average temperature curve).

A flat wafer removal profile 810 is indicated by a first differentialtemperature DT₀ of a first average temperature curve 815. As usedherein, the first differential temperature DT₀ may be referred togenerally as a “flat wafer differential temperature”. A concave waferremoval profile 820 is indicated by a second differential temperatureDT₁ of a second average temperature curve 825. The polishing pad isremoving more material at the center of the wafer relative to the edgesof the wafer in comparison with the flat wafer shape 810, resulting inthe second differential temperature DT₁ being greater than the firstdifferential temperature DT₀. A convex wafer removal profile 830 isindicated by a third differential temperature DT₂ of a third averagetemperature curve 835. The polishing pad is removing less material atthe center of the wafer relative to the edges of the wafer in comparisonwith the flat wafer shape 810, resulting in the third differentialtemperature DT₂ being less than the first differential temperature DT₀.

The wafer shapes 810, 820, 830 and the average temperature curves 815,825, 835 illustrate the general relationship between the wafer removalprofile and the differential temperature of the polishing pad. In otherembodiments, the wafer shapes 810, 820, 830 and the average temperaturecurves 815, 825, 835 may be any shapes and/or temperature curvesindicating the above relationship.

The first differential temperature DT₀ is set as a referencedifferential temperature for measured differential temperatures. In theexample embodiment, the first differential temperature DT₀ is determinedbased on historical data. For example, the first differentialtemperature DT₀ may be an average of past first differentialtemperatures DT₀. In other embodiments, the first differentialtemperature DT₀ may be determined by the temperature of the currentwafer. For example, the wafers may be polished until the differentialtemperature stabilizes or for a set number of wafers and then thecurrent differential temperature is set as the first differentialtemperature DT₀. Alternatively, the first differential temperature DT₀may be a pre-defined value.

FIG. 9 is an example average temperature profile 900 of a wafer producedby a single side polishing apparatus, such as the polishing apparatus100 shown in FIG. 1. The average temperature profile 900 may begenerated by the polishing apparatuses 100, 700 as described herein.Determining a differential temperature based on the average temperatureprofile 900 enables the controller 155 (shown in FIG. 1) toautomatically provide feedback for controlling the polishing headassembly 130 (shown in FIG. 1).

The average temperature profile 900 includes a first portion 910 and asecond portion 920. The first portion 910 is upset by the swingingmovement of the polishing head assembly 130. For example, a portion ofthe polishing head assembly 130 may periodically block or overlap thetemperature measurement of the temperature sensor 710 (shown in FIG. 7)on the polishing pad 150. Alternatively, the polishing head assembly 130does not block or overlap the temperature sensor 710. In the exampleembodiment, the second portion 920 is a smoother curve than the firstportion 910. In other embodiments, the first portion 910 and the secondportion 920 are reversed (i.e., as the distance increases, the firstportion 910 generally decreases and the second portion 920 generallyincreases). Alternatively, the average temperature curve may includeonly one portion 910, 920 or a plurality of alternative portions. In theexample embodiment, the second portion 920 is used by the controller 155to determine a differential temperature of the polishing pad 150 (shownin FIG. 1).

FIG. 10 is an enlarged view of a portion of the average temperatureprofile 900 and, more specifically, the second portion 920. Thecontroller 155 is configured to determine a wafer shape of the wafer W(shown in FIG. 1) based on analyzing the second portion 920 of theaverage temperature profile 900.

At least two temperature measurements are used to calculate adifferential temperature DT by:

DT=T _(A) −T _(B)  (1)

In the example embodiment, the differential temperature DT is calculatedusing Point A and Point B. Point A is a position X_(A) with asubstantially maximum temperature T_(A) with respect to the averagetemperature curve 900. Point B is a position X_(B) at which theresulting differential temperature DT is reliable. Point B has atemperature T_(B). In other embodiments, the differential temperature DTis calculated using temperatures from other points. In the exampleembodiment, Point B is approximately at the curve inflection point ofthe second portion 920. In some embodiments, Point B may be a fixeddistance from Point A. In other embodiments, Point B may be calculatedfor each wafer or a plurality of wafers.

The controller 155 is configured to dynamically calculate the positionsX_(A) and X_(B) in order to calculate a differential temperature DT_(i)for each polished wafer as described below. In some embodiments, thecontroller 155 may use historical or pre-defined positions X_(A) andX_(B).

Equation 2 is used to calculate the position X_(A) as:

$\begin{matrix}{X_{A} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}\; X_{{T\mspace{14mu} \max},i}}}} & (2)\end{matrix}$

The position X_(A) is the average of the first n maximum temperaturepositions X_(Tmax) at the beginning of the polishing pad 150's lifetime,where n is equal to the number of polished wafers after which the padbreak-in of the polishing pad 150 is completed and a characteristic padtemperature curve of the average temperature profile 900 (i.e., theaverage temperature profile after the pad break-in) is stabilized.Accordingly, for the first n wafers, the X_(A) value may change, butafter n wafers, X_(A) may generally become a fixed value for theremaining duration of the polishing pad 150's lifetime. Alternatively,X_(A) may continually change.

The temperature T_(A) corresponding to X_(A) is determined using theaverage temperature profile 900. In some embodiments, the position X_(A)may be extrapolated or rounded to a value of the average temperatureprofile 900. As such, both the position X_(A) and the temperature T_(A)may be automatically determined. In the example embodiment, thetemperature T_(A) is averaged to facilitate reduced inconsistentresults. For example, the average temperature T_(A) _(_) _(avg,i) ofPoint A for each wafer is calculated in Equation 3:

$\begin{matrix}{T_{{A_{—}{avg}},i} = \frac{T_{A,{i - 1}} + T_{A,i} + T_{A,{i + 1}}}{3}} & (3)\end{matrix}$

Temperatures T_(A,i−1), T_(A,i) and T_(A,i+1) corresponding to positionsX_(A,i−1), X_(A,i) and X_(A,i+1) for three wafers (e.g., W_(i−1), W_(i),W_(i+1)) are determined and averaged to generate the average temperatureT_(A) _(_) _(avg,i).

The position X_(B) is determined by Equation 4:

X _(B,i) =X _(A,i) +ΔX _(AB)  (4)

To calculate the temperature T_(B) of Point B, an A-B distance ΔX_(AB)(sometimes referred to as an “A-B offset”) is defined. In the exampleembodiment, the A-B distance ΔX_(AB) is pre-defined. The A-B distanceΔX_(AB) may be based on the vertical distance between the temperaturesensor 710 (shown in FIG. 7) and the polishing pad 150. In otherembodiments, the controller 155 may dynamically determine the A-Bdistance ΔX_(AB) such as, for example, using curve analysis to identifythe curve inflection point of the average temperature profile 900.Alternatively, the A-B distance ΔX_(AB) may be based on historical dataof the A-B distance ΔX_(AB). Hence, the position X_(B), for each wafer,is the sum the position X_(A) and the A-B distance ΔX_(AB) as expressedin Equation 4. Equation 4 is:

The temperature T_(B) for each wafer may be determined with the positionX_(B). In the example embodiment, similar to the average temperatureT_(A) _(_) _(avg), an average temperature T_(B) _(_) _(avg) iscalculated for each wafer using Equation 5:

$\begin{matrix}{T_{{B_{—}{avg}},i} = \frac{T_{B,{i - 1}} + T_{B,i} + T_{B,{i + 1}}}{3}} & (5)\end{matrix}$

Similar to Equation 3, Equation 5 averages temperatures T_(B,i) andT_(B,i+1) to produce the average temperature T_(B) _(_) _(avg).

Once the temperatures T_(A) _(_) _(avg) and T_(B) _(_) _(avg) aredetermined for each wafer, the differential temperature DT_(i) for eachwafer may be computed by Equation 6:

DT _(i) =T _(A) _(_) _(avg,i) −T _(B) _(_) _(avg,i)  (6)

In the example embodiment, the last k differential temperatures DT areused to calculate an average differential temperature DT_(avg) to becompared to the flat wafer differential temperature DT₀ shown in FIG. 8.Averaging the last k differential temperatures enables the controller155 to adjust the removal profile of the subsequent wafers withoutovercompensating for minor variations of the differential temperature ofthe current wafer. In other embodiments, the average differentialtemperature DT_(avg) is not calculated and each wafer's actualdifferential temperature DT is compared to the flat wafer differentialtemperature DT₀. The average differential temperature is calculated as:

$\begin{matrix}{{DT}_{avg} = {{\frac{1}{k}{\sum\limits_{i = 1}^{k}\; {DT}_{i}}} = \frac{{DT}_{1} + {DT}_{2} + \ldots + {DT}_{k}}{k}}} & (7)\end{matrix}$

where k is usually equal to the number polished wafers.

The controller 155, using the flat wafer differential temperature DT₀ asa reference, determines if the average differential temperature DT_(avg)indicates a flat wafer removal profile. In the example embodiment, thecontroller 155 selectively varies the pressure within the chamber 176 ofthe polishing head assembly 130 to alter the removal profile of thewafer W.

FIG. 11 is a method 1100 for varying a removal profile of a wafer duringpolishing using a polishing apparatus shown in FIG. 1. The polishingapparatus collects thermal data from a polishing pad and varies theremoval profile of the wafer based at least in part on the thermal data.The method may include additional, fewer, or alternate actions,including those discussed elsewhere herein.

The method begins with a temperature sensor collecting 1110 thermal datafrom a portion of a polishing pad. In the example embodiment, theportion of the polishing pad is a radius of the polishing pad. Thetemperature sensor transmits 1120 the thermal data to a controller. Thecontroller determines 1130 the removal profile of the wafer based atleast in part on the thermal data.

In the example embodiment, the controller generates an averagetemperature profile for the wafer using the thermal data. The controllerdetermines a differential temperature of the average temperatureprofile. After a set of wafers have been polished and a differentialtemperature is determined for each wafer, an averaged differentialtemperature is calculated. The averaged differential temperature iscompared to a reference differential temperature such as a flat waferdifferential temperature. In other embodiments, the averageddifferential temperature is not calculated and each differentialtemperature is compared to the reference differential temperatureseparately. The controller may compute the reference differentialtemperature based on the thermal data and/or the differentialtemperatures of the wafers. Alternatively, the controller stores apre-defined reference differential temperature.

The differences between the averaged differential temperature and thereference differential temperature indicate the removal profile of thewafer. For example, if the reference differential temperature is a flatwafer differential temperature, if the averaged differential temperatureis greater than the reference differential temperature, the averageddifferential temperature may indicate a concave removal profile. If theaveraged differential temperature is lower than the referencedifferential temperature, the averaged differential temperature mayindicate a convex removal profile.

The controller operates 1140 a polishing head assembly to position thesilicon wafer in contact with the polishing pad and to selectively varythe removal profile of the silicon wafer. The removal profile is variedto generally approach a reference removal profile (e.g., a flat removalprofile) indicated by the reference differential temperature.Alternatively, the removal profile may be varied to a different removalprofile. In the example embodiment, the controller communicates with apressurizing source to vary a pressure within a cap of the polishinghead assembly that is in contact with the wafer. The changing pressurecauses the cap to change shape and the removal profile of the wafer tochange in response. In some embodiments, the controller may communicateto the polishing head assembly to increase or decrease a polishingpressure on the wafer. Alternatively, the controller may change therotation speed of the polishing head assembly and/or the polishing pad.

FIG. 12 is a graph 1200 of an example experiment using a single sidepolishing apparatus shown in FIG. 1. The graph 1200 illustrates thedifferential temperature of each of a plurality of wafers over apolishing pad's lifetime. The example experiment implemented a methodsuch as the method 1100 shown in FIG. 11 to control the removal profilesof the plurality of wafers using a polishing pad's temperature.

In the example experiment, the differential temperatures of the initialwafers vary more than the later wafers. The initial variance may becaused by the pad break-in and/or a pre-existing rough, convex, orconcave surface on the wafer. After approximately 30 wafers, thedifferential temperature DT becomes stable as the differentialtemperature approaches the flat wafer differential temperature DT₀. Thedifferential temperature DT may stabilize after more or fewer number ofwafers.

In the example experiment, some differential temperature values may beconsidered as “outliers”. For example, the graph 1200 includes outliers1210. The outliers 1210 generally occur when the polishing apparatus isidling and the pad temperature drops. The initial wafers exhibited alower differential temperature during pad break-in. The outliers 1210may lead to inconsistent data such as, for example, in embodiments inwhich the flat wafer differential temperature DT₀ and/or the averagedifferential temperature DT_(avg) are based on historical or currentthermal data.

In order to reduce and/or remove outliers 1210, a threshold temperatureT_(Thre) may be determined as described below. In the exampleembodiment, the threshold temperature T_(Thre) is a dynamic valueupdated for each wafer. Alternatively, the threshold temperatureT_(Thre) may be a fixed value such as a pre-defined value. The thresholdtemperature T_(Thre) is compared to a temperature value of the averagetemperature profile of a wafer to determine if the thermal data of thewafer is an outlier 1210. The threshold temperature T_(Thre) enables acontroller to discard temperature readings below that limit. In otherembodiments, a temperature range may be determined. In the exampleembodiment, the threshold temperature T_(Thre) is not implemented untilthe differential temperature of the polishing pad has stabilized (i.e.,after the pad break-in). Alternatively, the threshold temperatureT_(Thre) may be implemented for the duration of the polishing pad'slifetime.

An effective temperature T_(Eff) of the current wafer is calculated inEquation 8 as:

$\begin{matrix}{T_{{Eff},i} = {\frac{1}{\Delta \; X_{AB}}{\int\limits_{X_{A}}^{X_{B}}{T_{i}{dx}}}}} & (8)\end{matrix}$

Using the values from calculating the differential temperature DT ofeach wafer, the effective temperature T_(Eff) of the current wafer isthe average temperature between the position X_(A) of the point A andthe position X_(B) of the point B, where T_(i) is an average temperatureprofile of the current wafer. The effective temperature T_(Eff) is usedto calculate a threshold temperature T_(Thre) and compared to thethreshold temperature T_(Thre). If the effective temperature T_(Eff) isless than the threshold temperature T_(Thre), the current wafer'stemperature measurements may not be representative of the currentwafer's removal profile (e.g., the polishing pad is idling).

The threshold temperature is expressed by Equation 9:

$\begin{matrix}{T_{Thre} = {\frac{C}{n}{\sum\limits_{j = {i - 1}}^{i - 1 - n}\; T_{{Eff},j}}}} & (9)\end{matrix}$

where n is generally the number of wafers for the pad break-in, and C isa correction factor lower than 1. In some embodiments, n is a differentvalue than the number of wafers for pad break-in. By averaging the lastn effective temperature T_(Eff) values and applying the correctionfactor C, the threshold temperature T_(Thre) is determined.

In the example embodiment, when the effective temperature T_(Eff) of thecurrent wafer is lower than the threshold temperature T_(Thre), thecorresponding differential temperature DT is discarded and replaced withthe last valid DT to compute the DT_(avg). In other embodiments, thecorresponding differential temperature DT is replaced an alternativedifferential temperature.

The embodiments described herein provide the ability to vary a removalprofile of a silicon wafer based on thermal data of a portion of thepolishing pad to enable an efficient and economical polishing method ofprocessing semiconductor wafers. The method facilitates improved waferyield and process capability, while reducing product tolerances and thetime needed to identify convex or concave removal profiles. Anotheradvantage of using the embodiments described herein includes the abilityto automate adjustments to the removal profile by compensating forinitially uneven wafer surfaces by modulating the shape of a polishinghead of the polishing assembly and using the thermal data as feedback.

When introducing elements of the present invention or the embodiment(s)thereof, the articles “a”, “an”, “the” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising”,“including” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements. The useof terms indicating a particular orientation (e.g., “top”, “bottom”,“side”, “down”, “up”, etc.) is for convenience of description and doesnot require any particular orientation of the item described.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description and shown in theaccompanying drawing[s] shall be interpreted as illustrative and not ina limiting sense.

What is claimed is:
 1. A polishing assembly for polishing of siliconwafers, the polishing assembly comprising: a polishing pad; a polishinghead assembly configured to hold a silicon wafer, the polishing headassembly configured to position the silicon wafer in contact with thepolishing pad and to selectively vary a removal profile of the siliconwafer; a temperature sensor configured to collect thermal data from aportion of the polishing pad; and a controller communicatively coupledto the polishing head assembly and the temperature sensor, thecontroller configured to receive the thermal data from the temperaturesensor and to operate the polishing head assembly to selectively varythe removal profile of the silicon wafer based at least in part on thethermal data.
 2. The polishing assembly of claim 1, wherein thetemperature sensor is an infrared (IR) camera.
 3. The polishing assemblyof claim 1, wherein the controller is further configured to determine anaverage temperature profile based on the thermal data, and to operatethe polishing head assembly to selectively vary the removal profile ofthe silicon wafer based at least in part on the average temperatureprofile.
 4. The polishing assembly of claim 1, wherein the thermal datacomprises thermal data of a radius of the polishing pad.
 5. Thepolishing assembly of claim 1, wherein the controller is configured todetermine a removal profile of the silicon wafer based at least in parton a comparison of the thermal data to a reference thermal value.
 6. Thepolishing assembly of claim 1, further comprising a turntable configuredto rotate the polishing pad.
 7. The polishing assembly of claim 1,wherein the polishing head assembly comprises a polishing head and acap, wherein the cap selectively varies the removal profile of thesilicon wafer.
 8. The polishing assembly of claim 7, wherein the capdefines a chamber, wherein the polishing head assembly selectivelyvaries the removal profile of the silicon wafer by regulating thepressure within the chamber.
 9. The polishing assembly of claim 8,further comprising a pressurizing source connected to the chamberconfigured to regulate the pressure with the chamber.
 10. The polishingassembly of claim 7, further comprising a retaining ring coupled to thepolishing head assembly and configured to receive the silicon wafer. 11.The polishing assembly of claim 10, wherein the retaining ring definesat least one circular opening configured to receive the silicon wafer.12. The polishing assembly of claim 10, wherein the polishing headassembly further includes a backing film positioned between theretaining ring and the polishing head assembly.
 13. The polishingassembly of claim 7, wherein the cap is made of at least one of plastic,aluminum, steel, ceramic, coated silicon, alumina, and silicon carbide.14. The polishing assembly of claim 13, wherein the cap includes afloor, wherein the polishing head assembly selectively varies theremoval profile of the silicon wafer by regulating the shape of thefloor.
 15. The polishing assembly of claim 14, wherein the cap furtherincludes an annular wall coupled to the polishing head and the floor,the polishing head, the floor, and the annular wall define a chamber,wherein the polishing head assembly selectively varies the removalprofile of the silicon wafer by regulating the pressure within thechamber.
 16. The polishing assembly of claim 15, further comprising apressurizing source connected to the chamber configured to regulate thepressure with the chamber.
 17. The polishing assembly of claim 1,wherein the temperature sensor is located adjacent to the polishing pad.18. The polishing assembly of claim 1, wherein the temperature sensor ispositioned to capture thermal data from at least a segment of thepolishing pad.
 19. The polishing assembly of claim 18, wherein thetemperature sensor is positioned to capture thermal data from a segmentalong a first diameter of the polishing pad.
 20. The polishing assemblyof claim 19, wherein the temperature sensor is positioned to capturethermal data from at least one of a second diameter of the polishingpad, a chord of the polishing pad, a linear portion of the polishingpad, an area of the polishing pad, and a non-linear portion of thepolishing pad.